Umbilical venous and arterial catheterisation — formative SAQs

1. Vessel anatomy and catheter courses

The umbilical stump carries two thick-walled, small-lumen arteries and one thin-walled, large-lumen vein. The umbilical venous catheter enters the umbilical vein, passes through the left branch of the portal vein and the ductus venosus, and emerges in the inferior vena cava just beneath the right atrium; its tip belongs at the inferior vena cava and right atrium junction at the diaphragm, around the eighth to ninth thoracic vertebra. The umbilical arterial catheter enters the umbilical artery, runs down the internal iliac (hypogastric) artery to the common iliac artery, and ascends the descending aorta; its tip belongs high, between the sixth and ninth thoracic vertebrae, with a low position at the third to fourth lumbar vertebra used only when a high position is unattainable. ^[9]

2. The Shukla formula and the calculation

The Shukla and Ferrara birth-weight formula estimates both depths. The umbilical arterial catheter length equals three times the birth weight in kilograms plus nine centimetres, and the umbilical venous catheter length equals half of that value plus one centimetre. For a 1000-gram infant, the weight is 1.0 kg, so the arterial length is 3 × 1 + 9 = 12 cm, and the venous length is half of 12, which is 6, plus 1 = 7 cm. Body-measurement and surface-anatomy methods — such as the umbilicus-to-nipple distance minus one centimetre for the venous line — can improve first-attempt accuracy, but the Shukla formula is the examination answer and the bedside starting point. ^[1]

3. The preferred arterial position and the venous target

The high arterial position between T6 and T9 is preferred because it sits in a wide segment of the descending aorta above the origin of the celiac, superior mesenteric, and renal arteries, where the catheter is bathed in fast flow and the risk of occluding a branch artery is low. The Cochrane review of high versus low position found no evidence to support a low position and concluded that high catheters should be used, because the high position carries a lower incidence of vascular complications without any rise in death, intraventricular haemorrhage, or necrotising enterocolitis. The venous target on radiograph is the diaphragm at T8 to T9 — above the ninth thoracic vertebra is too high and below the tenth is too low. ^[7]

4. Catheter sizing and tip confirmation

A 1000-gram infant is under 1500 grams, so the arterial catheter is 3.5 French (a 5 French catheter is used over 1500 grams); the venous catheter is usually 5 French, with a double-lumen line chosen if two lumens are needed at once. The tip is confirmed on an anteroposterior chest and abdomen radiograph (with a lateral view when the AP leaves doubt) before any use, and any malposition — a venous tip in the portal system or the heart, or an arterial tip in a branch or low position — is repositioned. Bedside ultrasound or echocardiography resolves the venous tip when the radiograph is uncertain, and reduces the rate of complications when used routinely. ^{[9] [11]}